Season 3 for me. The characters were fully developed, the shows running gags were in full force (Al never getting to eat, hating fat women, Kelly being dim, Bud a wise-ass, Al hating sex with Peg, Al making fun of Marcy, etc.)

Al's sarcasm the first few seasons was immense. Al was great through all of the seasons, but he had a different sort of comedy going on in the first few seasons that was abandoned for more slapstick and crude humor in later seasons.